Cusser
+1y
I find wiring pretty straightforward in most cases on vehicles on this vintage, but agree that there could be more information even in the official service manuals and wiring diagrams. Get a $5 12 volt test light and a decent $15 digital multimeter.
Like in the mid-1990s (before Internet, at least for me) even with the '88 Service Manual I had a "dickens" of the a time trying to find the actual location of the Malfunction Indicator wires so I could swap the leads at 60K miles. The drawing in the manual was so close-up that I couldn't even determine if that was in the cab or in the engine compartment !!!
To look towards adding aftermarket cruise control, I posted and even PM'd a few calling themselves Master Nissan Technicians to try to get a lead where the VSS (vehicle speed sensor) wire was on my 2004 Frontier. I could tell it was a green wire with a black stripe, couldn't find it on the ECM (which had real-cramped access anyway, even with harness disconnected). Anyway, finally pulled the instrument cluster rearward, found it (and the tach wire but didn't need that because I found VSS); so I soldered a labeled pigtail wire onto it, dropped it under the dash for the future.
I think a lot of today's technicians are just parts replacers.